Tone generators and generation of tones are known. Such apparatus and methods are used in music synthesizers and products such as some keyboard instruments and the like. Tone generators, i.e., sine wave generators, are also used for testing and calibration of more complex systems, e.g., integrated circuit transceivers and systems, found in cell phones and the like. By including a tone generator that is integral to or integrated with these systems, the systems can be arranged to essentially self test and calibrate with the application of power and little if anything else coupled to the system. A tone generator that is integral with a system needs to be highly efficient in terms of silicon usage and even minor improvements in silicon area can be significant, since the tone generator is, for the most part, overhead and contributes little if anything to the functionality of the actual system.
Furthermore it is important that the properties of the generated tone be adjustable over wide ranges of characteristics. One known way to generate a tone is to store values corresponding to the tone in read only memory. If one stores values at a maximum sampling rate and corresponding to a lowest desired frequency one will be able to read out those values and thus generate a digital tone at the lowest desired frequency or at frequencies that are integer multiples of that lowest frequency, e.g., every other value will be a tone at twice the lowest frequency. This technique takes significant silicon area and usually does not provide sufficient flexibility in tone characteristics.